A number of different mobile access networks have been developed and are deployed around the world. Around the world, the primary mobile access networks for cellular telephony are based on one of two families of standard communications protocols: Code Division Multiple Access (“CDMA”) and Global System for Mobile Communications (“GSM”). Cellular networks operating in one of these two standards provide telecommunication services to the users of mobile handsets or “cell-phones” in most countries in the world. Cellphones that operate on one or both of these types of networks are well-know in the art.
WiFi is another type of mobile access network that has been implemented in the IP domain. In WiFi networks, access points or “hot-spots” provide user of mobile computers, PDA's and WiFi compatible telephony handsets with the ability to connect to the Internet and communicate with other users using data transfers such as e-mail or instant messaging (“IM”) or voice over IP (“VoIP”) protocols. WiFi began as a method and system for enabling users to create wireless local area networks (“wireless LAN”) in order to wirelessly communicate with one another such as computers within a home or office. The most widely used wireless LAN technology is based on the IEEE 802.11 protocol which is known as WiFi. WiFi has increasingly become a method for mobile users to communicate with the Internet and make and receive VoIP calls. There are various versions of the IEEE 802.11 protocol in use, such as 802.11(a), 802.11(b) and 802.11(g). WiFi can transmit data up to approximately 320 feet indoors and 400 feet outdoors at speeds up to 54 million bits per second (“mbps”).
Worldwide Interoperability for Microwave Access (“WiMax”) is a more recent wireless LAN communication protocol known as 802.16. WiMax can transmit data up to approximately 70 mbps with a radius of approximately 30 miles. With such a communication radius a user could travel a significant distance and remain within reach of the access point and far fewer nodes would be needed to provide mobile communications to a user over a large area.
Recently, it has been proposed to have mobile handsets or cellphones that can operate in both the traditional cellular networks based on the various CDMA and GSM standards while also enabling a user to communicate with the Internet and place VoIP calls through WiFi and/or WiMax access points. As ubiquitous access becomes more prevalent, a mobile user equipped with a terminal or handset with multi-mode capabilities can move between heterogeneous access networks such as Bluetooth, 802.11X, WiMax, CDMA1XRTT, IPv6 and cellular (CDMA, GSM) networks. As the mobile moves between networks, the signaling and radio access networks will be different in each access network. While there has been some prior work to take care of seamless handoff when a user moves between two IP networks with different access technologies, there has been little work on providing a seamless handoff when a mobile moves between IP and non-IP networks involving different radio access networks. For example a user may be equipped with a “combo-phone” that can be connected to both 802.11 type IP networks and non-IP cellular networks such as CDMA or GSM. Based on user's preference and position (e.g., at home or in the car), a combo-phone can actively communicate via either interface. However it is a key challenge to handover the existing session seamlessly from one interface to another interface as the mobile moves in and out of the network of a specific kind.
Different access technologies have different mechanisms to attach to each different access network. Each network needs certain specific ways to obtain network resources (e.g., configuration parameters) and it takes different amounts of time to provide such network resources. It is not always possible to pre-configure all network information. Security requirements such as authentication of users are different for different access networks. Intra-technology mobility management and/or roaming vary between access networks. Supporting seamless mobility between heterogeneous networks is a challenging task since each access network may have different mobility, Quality of Service (QoS) and security requirements. Moreover, interactive applications such as VoIP and streaming media have stringent performance requirements on end-to-end delay and packet loss. The handover process places additional stress on these performance criteria by introducing delays due to discovery, configuration and binding update procedures associated with mobility events. Performance can also be tied to the specific access networks and protocols that are used for network access. Movement between two different administrative domains raise additional challenges since a mobile handset will need to re-establish authentication and authorization in the new domain.
Currently there are several initiatives to optimize mobility across heterogeneous networks. The MOBOPTS working group within the Internet Research Task Force (IRTF) and the Detecting Network Attachment (DNA) group within the Internet Engineering Task Force (IETF) are investing ways to support handover by using appropriate triggers from the lower layers. These initiatives deal only with issues of mobility between IP networks and do not provide solutions for mobility between heterogeneous (e.g., IP and Non-IP) networks.
The IEEE 802.21 working group has created a framework that defines a Media Independent Handover Function (MIHF) to facilitate the handover across heterogeneous access networks and help mobile users to experience better performance during seamless handover. This MIHF provides assistance to underlying mobility management approaches by allowing information about neighboring networks, link specific events and commands that are necessary during the handover process. The goal of IEEE 802.21 is to facilitate mobility management protocols such that the following handover requirements are fulfilled. One goal of IEEE 802.21 is to provide service continuity thereby minimizing the data loss and break time without user intervention. IEEE 802.21 supports applications of different tolerance characteristics. IEEE 802.21 provides a means of obtaining QoS information of the neighboring network. IEEE 802.21 provides a means of network discovery and selection. Network information could include information such as link type, link identifier, link availability, link quality. Selection of an appropriate handoff network can be based on required QoS, cost, user preference, etc. Power management can be accomplished by providing real-time link status. IEEE 802.21 does not provide a complete handover solution, but rather, is only a means to assist handover implementations.
The MIHF of 802.21 provides abstracted services to higher layers by means of a unified interface. This unified interface exposes service primitives that are independent of the access technology. The MIHF can communicate with access specific lower layer Media Access Control (“MAC”) and Physical Layer (“PHY”) components including those using IEEE 802.16, 802.11 and cellular protocols. The MIHF defines three different services: Media Independent Event Service (MIES), Media Independent Command Service (MICS) and Media Independent Information Service (MIIS).
Media Independent Event Service provides services to the upper layers by reporting both local and remote events. Local events take place within a client whereas remote events take place in the network. The event model works according to a subscription and notification procedure. An MIH user (typically upper layer protocols) registers to the lower layers for a certain set of events and is notified as those events take place. In the case of local events, information propagates upward from the MAC layer to the MIH layer and then to the upper layers. In the case of remote events, information may propagate from the MIH or Layer 3 Mobility Protocol (L3MP) in one stack to the MIH or L3MP in a remote stack. Some of the common events defined include “Link Up”, “Link Down”, “Link Parameters Change”, “Link Going Down”, “L2 Handover Imminent” among others. As the upper layer is notified about certain events it makes use of the command service to control links to switch over to a new point of attachment.
Media Independent Command Service (MICS) provides higher layers with MICS primitives to control the function of the lower layers. MICS commands are used to gather information about the status of the links, as well as to execute higher layer mobility and connectivity decisions from the lower layers. MIH commands can be both local and remote. Some examples of MICS commands are MIH Poll, MIH Scan, MIH Configure and MIH Switch. The commands instruct an MIH device to poll connected links to learn their most recent status, to scan for newly discovered links, to configure new links and to switch between available links.
Media Independent Information Service defines information elements and corresponding query-response mechanism to allow an MIHF entity to discover and obtain information relating to nearby networks. The MIIS provides access to both static and dynamic information, including the names and providers of neighboring networks as well as channel information, MAC addresses, security information and other information about higher layer services helpful to handover decisions. This information can be made available via both lower and upper layers. In some cases certain layer 2 information may not be available or sufficient to make intelligent handover decisions. In such scenarios, higher-layer services may be consulted to assist in the mobility decision-making process. The MIIS specifies a common way of representing information by using standard formats such as XML (external markup Language) and TLV (Type-Length-Value). Having a higher layer mechanism to obtain the information about the neighboring networks of different access technologies alleviates the need for a specific access-dependent discovery method.
It is, therefore, desirable to provide a method and mechanism for providing a seamless handoff when a mobile user using a mobile handset moves from an IP network such as a WiFi network to a non-IP cellular network such as a CDMA or GSM network, or vice versa.
It is desirable to address the issues of differing attachment mechanisms, allocation of network resources, timing, security and roaming when a mobile user transfers from using an IP network to a non-IP network or vice versa thereby avoiding packet loss.
It is desirable to take advantage of the MIHF of the emerging IEEE 802.21 standard in order to implement seamless handoff between heterogeneous networks.